Semiconductor devices are fabricated on wafers usually made out of silicon. The wafers are then cut into individual substrates, tested, and then packaged. There are many different ways of packaging a substrate, including Ball Grid Arrays (BGA), Flip Chip, Multi-chip Modules, Chip-on-a-Board, etc. Many of these packaging techniques involve grasping the substrate with a vacuum pickup from one location, manipulating the substrate in some way, and then placing it back down onto another or the same location. For example, when using flip chip packaging, the substrate must be lifted from a tray containing the substrates, flipped, and then solder balls are mounted onto pads located on the substrates.
In order for the vacuum pickup to obtain a good temporary bond with the substrate, the substrate should be horizontal with respect to the vacuum pickup. In some cases, when the substrates are lying on a substrate tray, the substrates are not lying perfectly horizontal because they may be fully seated within depressions built into the tray designed to hold the substrates. When the substrate is not fully horizontal with respect to the vaccum pickup the chances of the vaccum pickup being able to pick up the subtrate goes down. Shouls a subtrate not be picked up, intervention is often required to fix the positioning of the subtrate to permit the vaccum pickup to attach to the subtrate.
intervention is not desired in an efficient packaging process since it often requires stopping the packing process and a human operator making the required adjustments. Intervention slows down the process and increases overall production costs.
Solutions using custom designed subtrate trays can reduce the number of subtrates that are not lying horizontally, but they typically require a special tray for each size and type of subtrate. This increases the cost and overhead associated with the packing process, especially in packaging plants that process a wide variety of different subtrates.
Therefore, a need has arisen for a method and apparatus that can increase the probability of a vaccum pickup forming a solid bond with a subtrate by ensuring that the subtrates are lying horizontal with respect to the vacuum pickup.